Fever after vaccination is usually caused by the vaccine and is a normal systemic reaction to the entry of the heterologous protein into the body, and can usually be relieved within 1-2 days. However, if high fever or persistent fever occurs, it is recommended to seek medical attention promptly. I. The reason for fever after vaccination is that vaccines are foreign xenobiotics injected directly into the body without going through the process of digestion and decomposition. Generally, the body will have a certain degree of rejection reaction to foreign xenogeneic protein, but due to the small amount of xenogeneic protein in the vaccine, the rejection reaction caused is generally very mild and most people have no symptoms. In a few people, the immune reaction is a little stronger because of the difference in immunity of the body, which will stimulate the immune cells in the body to release endogenous pyrogen and cause fever in the hypothalamus. Second, the treatment method of fever after vaccination is 8-24 hours after vaccination, body temperature at 37.1-37.5℃ is a weak reaction, 37.6-38.5℃ is a moderate reaction, and higher than 38.5℃ is a strong reaction. Most of the reactions below moderate are seen, which usually last 1-2 days and can be relieved by themselves. If necessary, take proper rest, drink more boiled water, enhance body metabolism, pay attention to keep warm and prevent secondary infection. When fever of moderate degree or above occurs or lasts for more than 48 hours, physical methods of temperature reduction or symptomatic treatment with drugs can be used, such as wet compresses with ice packs wrapped in towels, rubbing alcohol and other physical cooling methods. It is also recommended to actively seek medical attention and follow medical advice to take oral acetaminophen, ibuprofen, aspirin and other non-steroidal anti-inflammatory drugs for antipyretic treatment. If during the vaccination period, there happens to be pathogenic microbial infections such as viruses, bacteria, mycoplasma or other non-infectious diseases that cause fever, such as wind-cold, upper respiratory tract infection or rheumatic immune disease, it can also cause fever and is a coincidental condition. In this case, a hospital visit is required to clarify the diagnosis, and the doctor will assess the situation as appropriate and provide symptomatic as well as cause-specific treatment based on the type of vaccine administered and the patient’s own condition. Avoid unauthorized use of medication that may affect the effectiveness of the vaccine.